Section 4 — Types of Inheritance

Dominant recessive inheritance

Interaction between dominant and recessive alleles
dominant alleles mask recessive alleles

What are three examples of dominant traits

widows peak, dimples, freckles

are dominant disorders common or uncommon and why
what is the one exception

dominant disorders are uncommon because many are lethal and result in death before reproductive age

huntingtons disease

huntingtons disease

dominant disorder but delayed action gene →person survives long enough to reproduce

Most genetic disorders are inherited as
3 examples

simple recessive traits → needs 2 recessive allles

taysachs, albinisim, cystic fibrosis

carriers

they are heterozygous for a recessive disorder (which needs 2 recessive alleles)

arent affected / display recessive disorder but can pass recessive allele to offspring

Incomplete dominance

heterozygous individuals show intermediate phenotype → mix of both

ex: TT = red tt= white Tt = pink

What type of inheritance is Sickle cell gene

incomplete dominance
SS = normal hemoglobin - no sickle cell disease

ss = aberrant/ irregular hemoglobin → sickle cell anemia

Ss = both normal and abnormal hemoglobin

Multiple allele inheritance

genes that exhibit more than 2 alleles form → but each person only gets 2 alleles still

there are more than two allele options for a gene

ABO blood grouping is what type of inheritance and explain it

multiple allele inheritance

Three alleles → iA iB i

iA and iB are codominant meaning that both are expressed if present

while i is recessive

iAiA or iAi → type a blood

iBiB or iBi → type b blood

iAiB → type ab blood

ii → type o blood

codominance

both alleles are fully expressed if present

TT = red tt = white Tt = both red and white appear

Sex linked inheritance

inherite traits are determined by genes on the sex chromosomes

more than 100 sexlinked disorders on the x chromosomeH

HOw many genes on x and y chromosomes

x- over 1400 genes (many for brain function)

y - 200 genes

X linked genes

found on x chromosomes
often passed from mother to son

Examples of x linked genes (2)

hemophilia / red green colorblindness

Which gender is x linked disorders easier to express in

males → males are XY → only one x chromosome so whatever allele they have → they express that

compared to females → XX → a normal dominant allele could mask the recessive disorder allele (carrier) → would need both alleles to be recessive to have the traiti

XAXA → unaffected female

XAXa → unaffected female but carrier

XaXa → affected

XAY → unaffected male male

XaY → affected male

Why are calico cats mostly female

coat color = determined by x chromosome

female cat has 2 X → 2 different x alleles with different colors → combination of both colors

male cats → 1X → can only show one color

Polygene inheritance

trait is controlled by several gene pairs at different locations working together

→ continous phenotype variation (wide range of phenotypese

examples of polygene inheritance

skin color, height, eye color → no clear main categories → ranges (no just black or white → range of colors)